1. Field of the Invention
The present invention relates to a method of high aspect ratio lithography, and more specifically to a method of smoothly performing a photolithography process of the device in a semiconductor process or an MEMS process, etc. high aspect ratio.
2. Description of the Related Art
Recently, there are many kinds of elements requiring a processing technology in a range of several tens or several hundreds microns, such as a high aspect ratio inductor for RF circuit by means of a semiconductor process, an optical switch for an optical internet by means of a micro-machine (MEMS) process, and a fluid device flowing path in the filed of bio-element. Such a high aspect ratio device is mainly formed when a surface of silicon or glass substrate formed on trench areas is etched into a deep trench. Then, a thin film is formed on trench areas such as a trench bottom and trench walls, and non-trench areas after forming the deep trench, at the same time, and then the thin film including the trench areas is patterned. However, many technical difficulties occur at the time of carrying out the above processes.
FIGS. 1A to 1C are cross-sectional views illustrating problems in depositing a liquid photoresist for forming a conventional high aspect ratio element. Here, liquid photoresist is liquid phase before coating on wafer and it transform into solid film phase after soft backing at temperature of 90 degree. It is a conventional photoresist for semiconductor process.
Referring to FIGS. 1A to 1C, a liquid photoresist 13 is deposited on a semiconductor substrate or a glass substrate 10, in which a high aspect ratio trench 12 is formed, by using a spin coating method. Metal film 14 is deposited on trench. When the photoresist is thinly deposited, as shown in FIG. 1A, the photoresist 13 is not attached around the trench 12 in the upper part of it, whereby the thin films may be exposed to a gas or a etchant in the subsequent etching process and unprotected areas from the gas or the solvent might be removed. When the photoresist 13 is thickly deposited, as shown in FIG. 1B, since the thick photoresist 13 must be developed, it is difficult to obtain a sharp pattern after developing. When the photoresist 13 remains on the trench 12, as shown in FIG. 1C, the photoresist is not surely attached to the upper part of the trench, and the photoresist film is not readily removed from the wall of the trench and the bottom of the thin film. The reason is that the thick photoresist 13 still covers the bottom and the wall of the trench after finishing the developing process of the upper portion of the trench. In this case, if the photoresist 13 left in the trench is completely developed, the pattern on the trench is developed along with the photoresist, thereby the pattern might be diminished or removed. Since there are a lot of specific problems to be solved by the present invention, in addition to the above problems in the art, the present invention is not limited to a solution for the problems mentioned above. Furthermore, the scope of the present invention includes a solution to general problems occurring in a photolithography process due to the high aspect ratio structure, and a solution for problems in blocking the trench forming the high aspect ratio structure and then depositing the thin film.